The ability to control tumor cell growth without serious side effects to the host organism has long been a goal in the continuing search for improved methods for treating cancer. Drugs or naturally occurring compounds usually have a broad range of activities towards different cells. Moreover, at concentrations which may be effective in inhibiting the growth of neoplastic cells, these compounds frequently demonstrate undesired effects on normal cells. Of particular interest therefore are compounds which selectively inhibit the growth of neoplastic cells while not inhibiting the growth of surrounding or other normal tissue.
Examples of such compounds are peptides such as the interferons and lymphocyte-derived tumor necrosis factor-.beta. (TNF-.beta.) as well as TNF-.alpha., derived from myelocytic cells, which display cytostatic and/or cytocidal activity against transformed cell lines, but do not affect normal cells. However, even with those compounds such as the interferons which show inhibitory activity primarily towards tumor cells, not all tumor cells respond to the compound. In addition, reliable methods have not been developed to identify tumors which have a high probability of responding to a given compound. Furthermore, there may be a fine line between a therapeutic dose of a given compound and that which is physiologically unacceptable or toxic. There has also been reported synergy between low levels of different types of IFN or of IFN and other growth inhibiting peptides, such as lymphocyte-derived TNF-.beta..
There is therefore an interest in being able to identify those tumor cells which may respond to a given anti-proliferative compound, and in being able to develop compositions which may be employed at low concentrations when administered therapeutically, while still providing the desired growth inhibitory effects, and with minimal deleterious effects on normal cells.